1. Field of the Invention
The present invention relates to a printing system and method used for fabricating a liquid crystal display device, and more particularly, to a printing system and printing method for fabricating a thin film transistor, a color filter, and a black matrix of a liquid crystal display device.
2. Description of the Related Art
In general, cathode ray tube (CRT) monitors are commonly used to display information on a computer displays and televisions because of the CRT monitor's superior picture quality and image brightness. However, as demand for larger displays increases, the size of the CRT monitors also increases. Accordingly, the overall size of the CRT monitor eventually increases to a point where it's size is too large to efficiently display image data. In addition, mobility of the CRT monitor decreases as overall weight of the CRT monitor increases.
Presently, flat type display devices, such as liquid crystal displays (LCD's), plasma display panel (PDP) displays, organic electro luminescence (EL) displays, light emitting diodes (LEDs), and field emission displays have gained in popularity. Among the different flat panel display devices, liquid crystal display (LCD) devices have been developed as monitors for laptop and desktop computers because or their low power consumption.
FIG. 1 is a cross-sectional view of an LCD device panel according to the conventional art. In FIG. 1, the LCD device panel is formed of a lower substrate and an upper substrate. The upper substrate includes a glass substrate 10 having a color filter layer 11, a black matrix 12, an orientation layer 14, and a common electrode 13. Both the black matrix 12 and the color filter layer 11 are formed on the glass substrate 10, wherein the black matrix 12 is disposed between adjacent color filter layers 11. The color filter layer 11 includes a resin film containing dye or three basic colors of red, green, and blue or a pigment thereof. An overcoat film (not shown) is provided for smoothing the color filter layer 11 and improving an adhesive force with the common electrode 13, which is commonly formed or a transparent conductive material, such as indium tin oxide (ITO). The orientation layer 14 aligns a liquid crystal material formed between the upper and lower substrates.
In FIG. 1, the lower substrate includes a glass substrate 10 having a thin film transistor (TFT) formed thereon, a protection film 20, a pixel electrode 21, and an orientation layer 14. The TFT includes a gate electrode 15, an active layer 16, a source electrode 18, and a drain electrode 19. The gate electrode 15 is formed on the glass substrate 10 with a gate insulating layer 17 formed on the gate electrode 15 and the glass substrate 10. The active layer 16 includes a semiconductor layer 16a formed by depositing an amorphous silicon (a-Si) and a n+ doped ohmic contact layer 16b at opposing upper portions of the semiconductor layer 16a. The protection film 20 is formed to cover the TFT and the gate insulating film 17. The pixel electrode 21 is formed on the protection film 20 and is formed of a transparent conductive material, such ITO. The orientation layer 14 is formed on the pixel electrode 21 and the protection film 20. Polarizing films 22 are disposed on the outside surfaces of the upper and lower substrate respectively.
In FIG. 1, light transmittance through the liquid crystal layer formed between the upper and lower substrates is controlled by application of an electric potential on the common electrode 13 and the pixel electrode 21. The common electrode 13 commonly receives a constant potential, whereas the pixel electrode 21 receives a data signal to generate the electric field. The pixel electrode 21 receives the data signal when the TFT is turned on. Specifically, a data signal is supplied to the source electrode 18 of the TFT and is transmitted via the active layer 16a through the ohmic contact layer 16b when the gate electrode 15 is enabled by receiving a scan signal. Accordingly, the data signal is transmitted to the drain electrode 19 and applied to the pixel electrode 21, thereby generating the electric field in combination with the common electrode 13 and controlling the light transmitted through the liquid crystal layer.
Fabrication of the LCD device commonly includes a thin film deposition process, a photolithographic process, and an etching process that are repeatedly performed. Moreover, fabrication of the TFT, the color filter layer 11, and the black matrix 12 includes sequential printing processes of ink or photoresist materials. The printing processes include a gravure offset method and a transfer method depending upon how the photoresist material is applied to the upper and lower substrates. The gravure offset method includes steps of filling the photoresist material into a groove of a cliché, transferring the photoresist material filled in the groove onto a roller; and applying the transferred photoresist material onto the upper or lower substrate,
FIGS. 2A to 2D are cross-sectional views of a sequential printing process according to a gravure of offset printing method according to the conventional art. In FIG. 2A, a photoresist or ink material 29 is filled into a plurality of rectangular grooves 26 formed in a surface of a cliché, wherein the plurality of rectangular grooves are spaced apart to define a pattern. Next, any excess photoresist material 29 that remains on the surface of the cliché is removed by a doctor blade 27. Accordingly, the photoresist material 29 only remains in each of the plurality of rectangular grooves 26.
In FIG. 2B, a roller 25 is rolled across the surface of the cliché along a first direction so that individual photoresist material portions 24 of the photoresist material 29 (in FIG. 2A) that filled each of the plurality of rectangular grooves 26 (in FIG. 2A) are temporarily bonded onto a blanket 28 of the roller 25. Accordingly, the pattern of the photoresist-filled rectangular grooves 26 (in FIG. 2A) is transferred onto the blanket 28 as the individual photoresist material portions 24.
In FIG. 2C, the roller 25 is placed above a substrate 10 and the individual photoresist material portions 24 are transferred onto a surface of the substrate 10 corresponding to the pattern of the photoresist-filled rectangular grooves 26 (in FIG. 2A). The substrate 10 may be formed of a glass or plastic substrate material.
In FIG. 2D, the individual photoresist material portions 24 are completely transferred to the surface of the substrate 10, and the printing process is completed. Thus, the pattern of the grooves 26 (in FIG. 2A) is replicated onto the surface of the substrate 10.
FIGS. 3A to 3D are cross-sectional views of a sequential printing process according to a transfer method according to the conventional art. In FIG. 3A, a photoresist or ink material 29 is filled into a plurality of rectangular grooves 26 formed in a surface of a cliché, wherein the plurality of rectangular grooves are spaced apart to define a pattern. Next, any excess photoresist material 29 that remains on the surface of the cliché is removed by a doctor blade 27. Accordingly, the photoresist material 29 only remains in each of the plurality of rectangular grooves 26.
In FIG. 3B, a surface of a substrate 10, which may be formed of a glass or plastic material, is placed upon the surface of the cliché to contact uppermost surfaces of individual photoresist material portions 24 filled in each or plurality of rectangular grooves 26 (in FIG. 3A). Then, heat and/or pressure is applied to the substrate 10 and cliché to bond each of the individual photoresist material portions 24 onto the surface of the substrate 10. Accordingly, the pattern of the photoresist-filled rectangular grooves 26 (in FIG. 3A) is transferred onto the surface of the substrate 10 blanket 29 as the individual photoresist material portions 24.
In FIG. 3C, the substrate 10 is removed from the surface of the cliché, and the individual photoresist material portions 24 are transferred from the plurality of rectangular grooves 26 (in FIG. 3A) onto the surface of the substrate 10, thereby completing the printing process for forming the pattern.
In FIG. 3D, the substrate 10 is delivered to a position in which the individual photoresist material portions 24 are prepared for additional processing.
However, both the gravue and transfer printing methods according to the conventional art are problematic. Since the cliché is exposed to an ambient atmosphere in the gravue and transfer printing methods according to the conventional art, the cliché may become contaminated, thus causing contamination of the substrate 10 and possibly disrupting transfer of the photoresist pattern onto the substrate 10.